1. Technical Field
The present invention relates to an interior magnet linear induction motor that causes a driving target to move linearly by electromagnetic force.
2. Description of Related Art
A permanent magnet linear motor is provided with a primary-side armature and a secondary-side electromagnetic rail. The primary-side armature includes coils arranged between teeth, and the secondary-side electromagnetic rail is provided so as to face the armature. In the secondary-side electromagnetic rail, a plurality of permanent magnets is arranged in a line such that opposite magnetic poles face each other.
The permanent magnet linear motor causes a current to flow in the coils of the armature such that a magnetic field caused by the current intersects the magnetic flux generated by the permanent magnets of the electromagnetic rail, and causes the armature or the electromagnetic rail to undergo relative linear motion by an electromagnetic action. For permanent magnet linear motors, a surface permanent magnet (SPM) configuration in which a line of permanent magnets is arranged on the electromagnetic-field-side surface is the mainstream. In order to realize both low cogging force and high durability, an internal permanent magnet (IPM) configuration is created.
As a technology related to an IPM linear motor, a linear motor has been disclosed that includes a plurality of window-shape insertion apertures near a surface of a stator core, on which a plurality of permanent magnets are arranged, and in which the plurality of permanent magnets are inserted into the insertion apertures and fixed in place, the window-shape insertion apertures each being formed by leaving a thin portion serving as an outer frame (see, for example, Japanese Patent No. 2751684).
In addition, an interior magnet linear induction motor is provided with a primary-side armature and a secondary-side line of inductor teeth. The primary-side armature includes coils arranged between teeth, and the secondary-side line of inductor teeth is provided so as to face the armature and includes a plurality of tooth portions arranged at a constant pitch. Permanent magnets may be arranged in the line of inductor teeth or in the teeth side of the armature.
The interior magnet linear induction motor causes magnetic flux to be generated sequentially in the gaps between magnetic poles of the armature and the tooth portions of the line of inductor teeth, and causes the armature or the electromagnetic rail to undergo relative linear motion.
As a technology related to an interior magnet linear induction motor, a pulse motor has been disclosed in which a primary-side magnetic flux generation unit (an armature) includes a group of separate cores, permanent magnets, and a coil (see, for example, Unexamined Japanese Patent Publication No. 2-32750). The group of separate cores may be obtained by dividing a core into a plurality of cores in a certain direction so as to correspond to the gaps between the tooth portions, and both ends of the group of separate cores have magnetic poles that face tooth portions. Each of the permanent magnets is inserted between corresponding separate cores such that the magnetic poles of any adjacent two of the permanent magnets are opposite to each other. The coil is formed around the group of separate cores.
Here, a permanent magnet linear motor such as that disclosed in Japanese Patent No. 2751684 has superior thrust characteristics. However, in such a permanent magnet linear motor, since permanent magnets are arranged over the entire stroke, the number of magnets used is large and the manufacturing cost is high.
Furthermore, in such a permanent magnet linear motor, since the density of magnetic flux leakage due to the permanent magnets on the electromagnetic-field-side surface is high, maintenance is performed while taking various safety precautions.
An interior magnet linear induction motor demagnetizes to a lesser degree and has superior thrust characteristics than a PM motor, and uses a smaller number of permanent magnets than a permanent magnet motor. However, the thrust of an interior magnet linear induction motor per unit size is smaller than that of a permanent magnet motor and thus the range of application of an induction type motor to applications is limited.